Connectivity Fault Management (CFM), as described in IEEE Std 802.1ag-2007, is a key component of operation, administration, and maintenance for carrier Ethernet. IEEE 802.1ag specifies protocols, procedures, and managed objects for end-to-end fault detection, verification, and isolation. IEEE 802.1ag establishes managed objects, called Maintenance Associations (MAs), to verify the integrity of a single service instance by exchanging CFM messages. The scope of an MA is determined by its Management Domain (MD), which describes a network region where connectivity and performance is managed. Each MA associates two or more Maintenance Association Endpoints (MEPs) and enables Maintenance Association Intermediate Points (MIPs) to support fault detection and isolation.
A continuity check protocol is used for fault detection. Each MEP periodically transmits Continuity Check Messages (CCMs) and tracks CCMs received from other MEPs in the same maintenance association.
Provider Backbone Bridging-Traffic Engineering (PBB-TE), as described in IEEE Std 802.1Qay-2009, was designed to provide full traffic engineering of paths in a bridged network. PBB-TE eliminates the need for backbone devices to perform learning and flooding. Instead of using Multiple Spanning Tree Protocol/Rapid Spanning Tree Protocol (MSTP/RSTP) for loop avoidance, PBB-TE uses a management plane or an external control plane to create static filtering table entries in the component bridges.
PBB-TE is a connection-oriented Ethernet technology that uses a statically configured tuple consisting of the ESP Destination Address (ESP-DA), ESP Source Address (ESP-SA), and ESP VLAN ID (ESP-VID) to create a PBB-TE path. The provisioned path is called an Ethernet Switched Path (ESP). Two co-routed point-to-point ESPs with the same Customer Backbone Port (CBP) MAC addresses form a bidirectional MAC service, which is called a point-to-point Traffic Engineering Service Instance (TESI).
PBB-TE supports 1:1 bidirectional path-protection switching. Two point-to-point TESIs are provisioned as a TE protection group (TEPG). One TESI is configured as a “working” TESI and the other as a “protection” TESI. In normal conditions, traffic is transmitted over the working TESI. In the event of either a failure of the working TESI or a specific administrative request, traffic is switched to the protection TESI.
Optionally, PBB-TE 1:1 protected paths may be configured to allow for load sharing. In load sharing mode, the TESIs that are assigned to a TE protection group can be re-used in a number of TE protection groups enabling a list of different backbone service instances to be distributed among a set of interdependent TE protection groups. In other words, in the load sharing mode, a TESI can be a protection TESI in one TE protection group and be a protection or working TESI in another protection group.
Each TESI is monitored by an independent MA, and each MA has two MEPs. One is located in a CBP of the near end; the other is located in a CBP of the far end. When the near end MEP detects the loss of CCMs, it notifies the far end MEP by sending a CCM with a Remote Defect Indicator (RDI) flag. Both ends are aware of the failure (either by loss of CCMs or receiving the CCM with the RDI flag), so protection switching to the protection TESI is executed on both ends. When the failure is cleared, traffic may be switched back to the working TESI or may stay in the protection TESI according to the configured mode (revertive or non-revertive).
Under certain equipment malfunction conditions and/or wrong configuration, a mismatch between mapping of backbone service instances to appropriate TESIs at the terminating CBPs may happen. To maintain the proper operation of the network, this mismatch should be detected and reported to the network operator. Then the network operator can clear the defect. There are two types of mismatch in 1:1 bidirectional protection switching:                Protection switching incomplete mismatch; and        Working/protection configuration mismatch.        
Protection switching incomplete mismatch may occur e.g. if the near end, due to a hardware malfunction, fails to switch over, but sends an RDI to the far end. The far end switches to the protection TESI while the near end is still in the working TESI. Similarly, a mismatch can also occur when the near end switches to the protection TESI, but the far end fails to switch when it receives the RDI.
A mismatch can also occur because of a wrong configuration. For example, one end may be configured to send traffic on the working TESI while the other end is configured to send traffic on the protection TESI. Similarly, one end may be configured in the revertive mode while the other end is configured in the non-revertive mode. In this case, the mismatch occurs when a failure is cleared.
PBB-TE supports protection of a group of TESIs traversing a common sequence of Provider Network Ports (PNPs). Such a sequence of PNPs, together with the intervening Bridge relays and LANs is called an infrastructure segment or sometimes simply a segment. The group of TESIs is protected from a connectivity failure occurring anywhere along the infrastructure segment, inclusive of the endpoint PNPs. The method of protection does not affect portions of the TESIs lying outside the segment; that is, the scope of protection is limited to the specified segment. This type of protection is called Infrastructure Segment Protection, which is specified in IEEE P802.1Qbf/D0.0.
There are two types of Infrastructure Protection Switching (IPS): 1:1 IPS and M:1 IPS. In 1:1 IPS a working segment and an associated protection segment are said to form an infrastructure protection group (IPG). In M:1 IPS additional protection segments are provided. Each such additional protection segment is called an alternate protection segment. An alternate protection segment can assume the role of the protection segment if connectivity failure of the protection segment has been detected. M:1 IPS requires that all segments associated with the IPG are mutually disjoint. Each provisioned Alternate Protection Segment is assigned a selection priority unique within the IPG. On detection of a failure associated with the protection segment, the role of the protection segment is assumed by the alternate protection segment having the highest (lowest numeric) priority and for which a connectivity failure has not been detected.
PBB-TE Infrastructure Segment Protection also supports load sharing mode in a manner similar to the TESI protection switching, enabling a segment to be associated with more than one IPG. For example, the operator may designate a Segment 1 as the working segment of an IPG1 and a Segment 2 as the protection segment of the IPG1. The operator may concurrently designate the Segment 2 as the working segment of an IPG2 and the Segment 1 as the protection Segment of the IPG2. In this case, the same MA provides monitoring of the Segment 1 in the IPG1 and in the IPG2.
The international patent application WO2009/127931 suggests using a traffic field in CCMs to indicate traffic status, e.g. whether traffic is transmitted in the TESI monitored by the CCMs. If the traffic field of received and transmitted CCMs of a MEP does not match for a predetermined period of time a mismatch is detected. However, the traffic field supported in PBB-TE MEPs may not be sufficient to detect a mismatch defect in a load sharing mode of PBB-TE 1:1 bidirectional path protection switching or PBB-TE Infrastructure Segment Protection. The traffic field can indicate whether or not there is traffic on a specific TESI or infrastructure segment, but in case of load sharing the traffic on the TESI of infrastructure segment may be associated with several different TE protection groups or infrastructure protection groups.